Facility for stripping a moving metal product by means of a picosecond laser

Abstract

Disclosed is a facility (6) for stripping a moving metal product (3), comprising: - a stripping assembly (8) having at least one picosecond pulse laser device (10), each configured to emit picosecond laser pulses onto the surface of the moving metal product (3) in order to strip it, - a control unit (12) suitable for acquiring information relating to the moving metal product (3) and configured to: - determine operating parameters to be applied to the stripping assembly (8) in order to achieve stripping of the oxide layer on the surface of the metal product (3) by emission, by each laser device (10), of picosecond laser pulses onto the metal product (3) surface, - apply these operating parameters to the stripping assembly (8) in order to strip the surface of the metal product (3).

Description

[0001] Installation for stripping a moving metal product using a picosecond laser

[0002] The present invention relates to an installation and a method for stripping a moving metallic product having an oxide layer on its surface.

[0003] By product, we mean a metallic product suitable for moving along a line, of any shape, including a strip, a sheet, a wire or a metal tube.

[0004] The metal product is, for example, made of stainless steel.

[0005] It is common for steel products, especially stainless steel, to undergo treatments that lead to the formation of an undesirable oxide layer on their surfaces at high temperatures, in contact with an oxidizing atmosphere such as air. The composition of these oxides varies considerably depending on the composition of the base metal and the conditions of their formation. Most commonly, oxides of the elements Fe, Cr, Mn, and Si are predominant.

[0006] The treatments that lead to this formation are, typically, but not exclusively, the reheating of a semi-finished product (ingot, slab, bloom, billet) before hot rolling and its subsequent exposure to air after hot rolling, as well as the various annealing processes at several hundred degrees Celsius that the product undergoes before, during, and / or after its cold rolling cycle (which may be carried out in one or more stages, some of which may be separated by an intermediate annealing), if these annealing processes take place in an atmosphere that is not perfectly inert or reducing. These undesirable oxides must, of course, be eliminated before the sheet or strip becomes a usable product or a semi-finished product ready to undergo the final shaping operations that will make it a usable product.It is also often important to remove these oxides before the first cold rolling stage, to prevent them from becoming embedded in the surface of the semi-finished product during rolling and leading to a poor surface finish.

[0007] It must be understood that the undesirable oxide layer referred to here is not the thin chromium oxide layer (known as the "passive layer") that forms spontaneously in air at room temperature on the surface of stainless steels and protects them from oxidation. The problematic oxide layer that we want to eliminate is the one that forms when the semi-finished or finished metal is exposed to high temperatures in an oxidizing atmosphere. Once this layer is removed, the surface of the stainless steel is exposed, and the protective passive layer of chromium oxides can quickly and spontaneously reform, restoring the steel to its stainless state under normal operating conditions.Mechanical descaling by shot blasting (projecting hard beads onto the surface to be treated) and / or by an oxide breaker (passing the strip between pairs of rollers that subject it to bending, compression, and tension) makes it possible to crack and easily remove a large portion of the oxides, for example by brushing, but may be insufficient to remove them all. Shot blasting also has the disadvantage of increasing surface roughness, which subsequent operations on the sheet metal or strip may not necessarily correct when this is undesirable.

[0008] Most conventionally, the unwanted oxide layer is removed by means of a chemical or electrolytic pickling process, or a succession of such pickling processes.

[0009] Chemical pickling is carried out in one or more baths of hydrofluoric, hydrochloric, sulfuric, or nitric acid. Electrolytic pickling is typically carried out in a sodium sulfate bath or an acid bath (nitric or sulfuric).

[0010] Chemical stripping is the most radical process for removing unwanted oxides. However, it has many drawbacks.

[0011] It consumes high quantities of acids, with, at most, very little possibility of recovering some of them for later reuse.

[0012] The infrastructure required for its execution, namely the successive pickling baths and their ancillary equipment, is expensive and bulky. It is not uncommon to encounter chemical pickling installations for conveyor belts up to 200 meters long.

[0013] These facilities use hazardous products, particularly hydrofluoric acid. Their polluting liquid and solid discharges (sludge containing oxides mixed with pickling liquids) must be stored and treated according to strict regulations, the stringency of which will only increase in the future, which is costly. The heated acid baths also release acidic vapors that must be neutralized. Nitric acid is also a source of NO emissions. X that must be captured and processed.

[0014] Electrolytic pickling processes are also used, carried out while the strip or sheet is immersed in a bath generally based on sodium sulfate, or nitric or sulfuric acid, which must also be treated after use. Electrolytic pickling requires a fairly expensive installation using a relatively large amount of electrical energy. It can be supplemented by chemical pickling with acid, which is less intensive than when chemical pickling alone is used, but which presents the same type of drawbacks as those mentioned above. Electrolytic pickling also produces sludge that must be stored, collected, treated, and then treated or recycled. The used baths must be treated. Finally, the presence of hexavalent chromium in solution in the pickling liquids represents a significant risk to the health of personnel and to the environment: its concentration in the liquids and personnel exposure are measured and monitored.

[0015] We therefore examined possibilities of replacing, at least in some cases, the chemical or electrolytic stripping of metal products with processes using a laser. The classic work "Laser Cleaning" (Boris Lukyanchuk, December 2002, ISBN: 978-981-02-4941-0) discusses such possibilities, particularly for cleaning works of art and buildings, i.e., for fixed surfaces. The laser beam is projected onto the surface to be cleaned and causes the oxide layer to detach.

[0016] In this way, the use of acids and / or sulfates is avoided, and there is no longer any need to reprocess sludge and polluting and dangerous liquids.

[0017] However, the use of existing technologies, coupled with CO2 or excimer lasers, does not allow for optimal results on industrial format scrolling strips or sheets, due to heavy maintenance, continuous or excessively long laser operating modes, and excessively high operating costs due to the number of lasers used, given the high scrolling speed of current lines.

[0018] Document EP3631049 A1 describes a process for stripping an oxide layer in which the composition of the oxide layer and its thickness are determined by laser-induced plasma spectroscopy.

[0019] This technique is unsatisfactory because it requires damaging the metal beneath the oxide layer. Furthermore, determining the thickness and composition of the oxide layer does not reliably determine the appropriate pickling parameters for removing it.

[0020] We also know from document WO2018 / 096382 a process and installation for laser stripping of metallic products.

[0021] This process determines the emissivity of the oxidized surface of the metal product to be cleaned by emitting a beam onto this surface using a first laser, intercepting the beams reflected by the oxidized surface, and analyzing these reflected beams. The operating parameters of the cleaning lasers are then adjusted according to the emissivity thus determined.

[0022] This process allows the energy emitted by the stripping lasers to be adapted to effectively remove the oxide layer present on the surface. A process is also known from document W02023 / 007221 in which an energy threshold for expelling the oxide layer is determined by emitting laser pulses of analysis with wavelengths and pulse durations equal to those of the stripping laser(s), and the evaluation, based on information gathered following this emission, of the energy density threshold for expulsion of the oxide layer.

[0023] This process is not entirely satisfactory, however. Indeed, the lasers used generate heat on the surface of the metallic product, such that re-oxidation of the product's surface can occur after the pickling process.

[0024] Consequently, it is necessary to check after laser stripping for any remaining unstripped areas and to perform a second stripping or even chemical stripping to achieve the desired surface finish. However, a second stripping process involves stripping the same area of ​​the product twice, risking damage to the metal, and chemical stripping presents the problems mentioned above.

[0025] One aim of the invention is therefore to propose a stripping process and installation which resolves the aforementioned disadvantages, in particular allowing the surface of the metal product to be stripped precisely in a single pass, so that no area of ​​the product is not stripped or stripped several times.

[0026] To this end, the invention relates to a stripping installation for a moving metallic product, the moving metallic product having at least one surface covered with an oxide layer, characterized in that the installation comprises:

[0027] - a stripping assembly comprising at least one picosecond pulsed laser device, each picosecond pulsed laser device being configured to emit picosecond laser pulses onto the surface of the moving metallic product to strip it,

[0028] - a control unit capable of acquiring information relating to the moving metal product, the information including the speed at which the metal product moves and at least one characteristic dimension of the metal product in a plane orthogonal to an axis of movement of the metal product, the control unit being configured to:

[0029] - determine operating parameters to be imposed on the stripping assembly to achieve the stripping of the oxide layer on the surface of the metallic product by emission by the laser device(s) of picosecond laser pulses onto the surface of the metallic product,

[0030] - to impose said operating parameters on said stripping assembly to strip the surface of the metal product. The operating parameters are determined based on information relating to the moving metal product acquired, including the speed of movement of the metal product and at least one characteristic dimension of the metal product in a plane orthogonal to an axis of movement of the metal product.

[0031] According to other advantageous aspects of the invention, the installation comprises one or more of the following features, taken individually or in any technically feasible combination: the picosecond laser pulses have a duration of between 0.1 and 30 ps, ​​in particular between 1 and 30 ps; the stripping assembly comprises a distribution system configured to shape the laser pulses and / or to move the laser pulses over the surface of the moving metal product such that the laser pulses emitted by the laser device(s) strip the oxide layer over the entire surface of the metal product as it moves.The distribution system is configured to shape and move laser pulses across the surface of the metallic product such that the laser pulses impact the surface of the metallic product along a plurality of lines, including straight, curved, or broken lines, or spots, including circular, rectangular, or square spots. For each laser device, the distribution system comprises at least one shaping device, preferably a Diffractive Optical Element (DOE), a Refractive Optical Element (ROE), a Multi-plane Light Conversion (MPLC) device, a Powell lens, or an optical homogenizer, configured to shape the laser pulses such that each laser pulse impacts the surface of the metallic product along the line or spot, with the energy density received along at least one direction on the line or spot being substantially uniform.The stripping assembly is configured so that the energy density received from the stripping assembly on each line or spot of the surface of the metal product is between 0.01 and 0.8 J / cm. 2 , particularly between 0.08 and 0.35 J / cm 2The distribution system includes, for each laser device, at least one scanning device configured to move the pulses generated by the associated laser device onto the surface of the metal product at a predetermined scanning speed and scan pitch, such that the pulses emitted by each laser device impact a predetermined portion of the metal product's surface. Each scanning device includes at least one scanner, such as a polygonal or galvanometric scanner. The distribution system includes a focusing element, such as a focusing lens like an f-theta lens or a parabolic mirror, configured to focus the shaped laser pulse onto the surface of the metal product, with the scanning device positioned between each shaping device and the focusing element.The laser device(s) is configured to emit picosecond laser pulses alternately along two separate optical paths, and the scanning device associated with the laser device includes at least two synchronized and phase-shifted polygonal or galvanometric scanners configured to move the pulses alternately generated by the associated laser device across the surface of the metallic product. Alternatively, the laser device(s) is configured to emit picosecond laser pulses along a single optical path, and the stripping assembly includes an external module, in particular an acousto-optic modulator (AOM) or an electro-optic modulator (EOM), configured to generate, from the laser pulses, laser pulses emitted successively along two separate optical paths.The operating parameters include the pulse energy of the laser device(s), the duration of the pulses received from the stripping assembly on the surface of the metal product, and the scanning speed and / or scan pitch of the scanning device. The control unit is configured to determine the operating parameters to be imposed on the stripping assembly to achieve stripping by expulsion of the oxide layer on the surface of the metal product by a single pulse at each treated point on the surface. These operating parameters are imposed on the stripping assembly to strip the surface of the metal product by expulsion of the oxide layer through the emission of a single pulse at each of these treated points.

[0032] Thus, preferably, the removal of the oxide layer is achieved at each point of the metallic surface following a single laser pulse received at that point, whether the laser pulses impact the surface of the metallic product according to a plurality of lines or spots.

[0033] In other words, a single laser pulse emitted by the laser device at a point on the surface of the metallic product is sufficient to completely remove the oxide layer. This is because the energy density received at each point by this laser pulse induces a shock wave that expels the oxide layer.

[0034] To this end, preferably, the installation includes a determination set configured to determine, on each of a plurality of successive sections of the moving metal product, an oxide layer expulsion energy density threshold, corresponding to a minimum energy density required to expel the oxide layer on the section considered by shock wave, and the control unit is configured to receive the expulsion energy density threshold, to determine the operating parameters to be imposed on the stripping set as a function of this density threshold, such that each point of the section considered is exposed in at least one instant to an energy density greater than or equal to the oxide expulsion energy density threshold, and to control the emission on the surface of the metal product by the stripping set of laser pulses of energy greater than or equal to the expulsion energy density threshold.

[0035] Thus, a single pulse, inducing a shock wave enabling the expulsion of the oxide layer, is necessary to remove the oxide layer at each point, without a change of state of matter.

[0036] In contrast, if the energy density received by all or part of the section or surface of the product is less than the expulsion energy density threshold, the oxide layer cannot be stripped over all of that section or surface.

[0037] In particular, the emission of several successive laser pulses on a spot or line such that the energy density received at that spot or line is less than the expulsion energy threshold for each pulse does not allow the oxide layer to be expelled at that spot or line.

[0038] Thus, by comparison, in devices of the prior art, the oxide layer is removed essentially by vaporization, by sublimation... and requires subjecting each point of the surface to a succession of pulses.

[0039] The energy required to produce this shock wave is determined by the expulsion energy density threshold measurement system.

[0040] Shock wave removal of the oxide layer is more productive, since each part of the surface is only passed over once, and more energy-efficient than other laser treatments. Indeed, prior art treatments use laser energy to change the state of the material to be ablated (from solid to liquid to gas) and require subjecting each point on the surface to a succession of pulses, necessitating a relatively high amount of energy. In contrast, the treatment according to the invention requires a significantly lower amount of energy to generate the shock wave.

[0041] According to one embodiment, the determination assembly comprises: an emission system including a laser source, the emission system being configured to emit, on a portion of said section considered, laser beams of analysis of wavelength and duration of beam equal to those of the laser stripping device(s), to form, within said portion, a stripped zone devoid of the oxide layer, an image acquisition system configured to acquire an image of the portion impacted by the laser beams of analysis, during the passage of the metallic product (3), a processing system configured to determine, from each image acquired by the image acquisition system, a representative dimension of the stripped zone and to evaluate, from said representative dimension and information relating to the energy profile of the laser beams of analysis, the threshold of energy density of expulsion of the oxide layer.

[0042] Preferably, the analysis laser wells are adapted to form, within the portion, a damaged area, on which the metal underlying the oxide layer has been damaged by the analysis laser wells, and the processing system is configured to determine, from this image, a representative dimension of the damaged area and to evaluate, from the representative dimension of the damaged area and information relating to the energy profile of the analysis laser wells, a metal damage energy density threshold, corresponding to the energy density above which degradation of the surface of the metallic product under the oxide layer is observed.

[0043] The processing system is preferably configured to transmit the damage energy density threshold to the emission system, and the emission system is configured to adapt the energy of the analysis laser beam according to the damage energy density threshold so that at any point in the impacted portion of the next section of the moving product, the energy density is less than the damage energy density threshold.

[0044] Information relating to the energy profile typically includes the shape of the energy profile and the energy or power of the analysis laser beams, and the laser stripping assembly includes a system for determining the shape of the energy profile of the analysis laser beams and / or a system for determining the energy or power of the analysis laser beams. The system for determining the shape of the energy profile of the analysis laser beams preferably includes a beam analyzer and an optical device, including a beam splitter, configured to deflect a portion of each analysis laser beam towards the beam analyzer, the beam analyzer being configured to evaluate the shape of the energy profile from the deflected portion of the analysis laser beam.

[0045] Preferably, the system for determining the energy or power of the analysis laser beams includes a power meter and an optical device, including a beam splitter, configured to deflect a portion of each analysis laser beam towards the power meter, the power meter being configured to evaluate the energy and / or power of the analysis laser beams from the deflected portion of the analysis laser beam.

[0046] The invention also relates to a method for stripping a metal product in motion, the metal product in motion having at least one surface covered with an oxide layer, characterized in that it comprises:

[0047] - the acquisition, by a control unit, of information relating to the moving metallic product, the information including a speed of movement of the metallic product and at least one characteristic dimension of the metallic product in a plane orthogonal to an axis of movement of the metallic product,

[0048] - the determination of operating parameters to be imposed on a stripping assembly comprising at least one picosecond pulsed laser device, in order to achieve the stripping of the oxide layer on the surface of the metallic product,

[0049] - the emission by the picosecond pulsed laser device or devices, of picosecond laser pulses on the surface of the moving metallic product to strip it, according to the operating parameters determined by the control unit.

[0050] The operating parameters are determined based on information relating to the moving metal product acquired, including the speed of movement of the metal product and at least one characteristic dimension of the metal product in a plane orthogonal to an axis of movement of the metal product.

[0051] According to other advantageous aspects of the invention, the method comprises one or more of the following features, taken individually or in any technically feasible combination: the picosecond laser pulses have a duration of between 0.1 and 30 ps, ​​in particular between 1 and 30 ps; the stripping assembly comprises a distribution system configured to shape the laser pulses and / or to move the laser pulses over the surface of the moving metal product; the method comprises shaping and / or moving the laser pulses over the surface of the metal product such that the laser pulses strip the oxide layer over the entire surface of the metal product as it moves.The distribution system shapes and / or moves laser pulses onto the surface of the metallic product such that the laser pulses impact the surface of the metallic product along a plurality of lines, including straight, curved, or broken lines, or spots, including circular, rectangular, or square spots. The distribution system comprises, for each laser device, a focusing element, including a focusing lens such as an f-theta lens or a parabolic mirror. The method includes focusing, by the focusing element, the shaped pulses so that the shaped and focused pulses impact the surface of the metallic product along a line or a spot, the energy density received along at least one direction on the line or spot being substantially uniform.The distribution system comprises, for each laser device, at least one shaping device, the shaping device preferably comprising a Diffractive Optical Element (DOE), a Refractive Optical Element (ROE), a Multi-plane Light Conversion (MPLC) device, a Powell lens, or an optical homogenizer, disposed between each laser device and the focusing element. The method comprises shaping the laser pulses by each shaping device such that the shaped pulses impact the surface of the metallic product along the line or spot, the energy density received along at least one direction on the line or spot being substantially uniform. The energy density received from the stripping assembly on each line or spot of the surface of the metallic product is between 0.01 and 0.8 J / cm². 2 , particularly between 0.08 and 0.35 J / cm 2The displacement of laser pulses shaped on the surface of the metal product is implemented by at least one scanning device. The scanning device moves the pulses generated by the laser device and shaped by the associated shaping device onto the surface of the metal product at a predetermined scanning speed and scan pitch, such that the pulses emitted by each laser device impact a portion of the surface of the metal product. The laser device(s) emit the picosecond laser pulses alternately along at least two distinct optical paths. The scanning device comprises at least two synchronized and phase-shifted polygonal or galvanometric scanners, and the polygonal or galvanometric scanners alternately move the pulses generated by the laser device onto the surface of the metal product to distinct positions on the surface of the metal product.The laser device(s) is / are configured to emit picosecond laser pulses along a single optical path, and the stripping assembly includes an external module, such as an acousto-optic modulator (AOM) or an electro-optic modulator (EOM), which generates successive laser pulses from the laser pulses along two separate optical paths. Operating parameters include the pulse energy of the laser device(s), the duration of the pulses received from the stripping assembly on the surface of the metal product, and the scanning speed and / or scan pitch of the scanning device.

[0052] The operating parameters to be imposed on the stripping assembly are determined so as to obtain stripping by expulsion of the oxide layer on the surface of the metal product by a single pulse at each treated point of the surface, and said operating parameters are imposed on said stripping assembly to strip the surface of the metal product by expulsion of the oxide layer by a single pulse at each treated point of the surface.

[0053] Thus, preferably, the removal of the oxide layer is achieved at each point of the metallic surface following a single laser pulse received at that point, whether the laser pulses impact the surface of the metallic product according to a plurality of lines or spots.

[0054] In other words, according to the process, a single laser pulse emitted by the laser device at a point on the surface of the metallic product is sufficient to completely remove the oxide layer.

[0055] To this end, preferably, the determination of operating parameters includes, on each of a plurality of successive sections of the moving metal product, the determination of an oxide layer expulsion energy density threshold on the section of the metal product under consideration, corresponding to a minimum energy density required to expel the oxide layer on the section under consideration, and the determination of the operating parameters to be imposed on the pickling assembly includes said energy density threshold, such that each point of the section under consideration is exposed in at least one instant to an energy density greater than the oxide layer expulsion energy density threshold.

[0056] According to one embodiment, the determination of the energy density threshold comprises: - the emission of analysis laser pulses by an emission system comprising a laser source, the analysis laser pulses being of equal wavelength and pulse duration to those of the laser stripping device(s), on a portion of the section considered, to form, within the portion, a stripped zone devoid of the oxide layer,

[0057] - capturing an image of the portion of the surface impacted by the laser scanning probes,

[0058] - the determination, from said image, of a dimension representative of the stripped area,

[0059] - the evaluation, based on said representative dimension and information relating to the energy profile of the analysis laser sources, of the expulsion energy density threshold of the oxide layer.

[0060] According to one embodiment, the emission from the analysis laser beams forms, within said portion, a damaged zone, on which the metal underlying the oxide layer has been damaged, and the method further comprises determining, from said image, a representative dimension of the damaged zone and evaluating, from the representative dimension of the damaged zone and information relating to the energy profile of the analysis laser beams, a threshold of energy density of metal damage, corresponding to the energy density above which a degradation of the surface of the metallic product, under the oxide layer, is observed.

[0061] The process preferably includes transmitting the damage energy density threshold to the emission system, and on the next section of the moving metallic product, the emission system emits an energy-scanning laser beam adapted such that at every point in the portion impacted by the scanning laser beams, the energy density is below the damage energy density threshold.

[0062] Typically, energy profile information includes the shape of the energy profile and the energy or power of the analysis laser sources.

[0063] The step of determining the expulsion energy density threshold of the oxide layer preferably includes determining the shape of the energy profile of the analysis laser beams and / or determining the energy or power of the analysis laser beams.

[0064] According to one embodiment, the step of determining the expulsion energy density threshold of the oxide layer includes determining the shape of the energy profile of the analysis laser beams, including deflecting a portion of each analysis laser beam to a beam analyzer and evaluating the shape of the energy profile by the beam analyzer.

[0065] According to one embodiment, the step of determining the expulsion energy density threshold of the oxide layer includes determining the energy and / or power of the analysis laser beams, including diverting a portion of each analysis laser beam to a power meter, and evaluating the energy and / or power of the analysis laser beams by the power meter.

[0066] The invention also relates to a continuous processing line for a metallic product comprising a pickling installation according to the invention.

[0067] The invention will be better understood upon reading the following description, given with reference to Figure 1, which schematically illustrates, in profile, a continuous line comprising a laser stripping installation according to an embodiment of the invention.

[0068] The laser pickling installations that will be described in detail and illustrated with examples will be described with reference to the treatment of a cold-rolled stainless steel strip in continuous motion, which has just undergone cold rolling and annealing on a continuous line. The laser pickling installation according to the invention, which performs the pickling function, is also integrated into this continuous line, either replacing or operating upstream of the electrolytic and / or chemical pickling installations usually used on this type of continuous line.

[0069] It goes without saying that the laser stripping installation 6 according to the invention which will be described can also be integrated into a continuous processing line comprising more or less equipment than that which will be described, or be the subject of a separate installation specially dedicated to this stripping.

[0070] Also not shown are the devices typically found on such lines that do not play a major metallurgical role and, in any case, do not directly participate in the laser stripping process carried out according to the invention. These include, in particular, pinch rollers for guiding the metal product and strip accumulators that act as buffers between certain devices, each of which may require a different metal product feed speed.

[0071] A continuous processing line comprising an installation according to an embodiment of the invention has been schematically illustrated in Figure 1.

[0072] This line first comprises a winding installation 1 for a coil 2 of a metallic product 3, typically hot-rolled stainless steel, whose thickness is usually on the order of a few tenths of a millimeter or a few millimeters, and whose width, defined between a first longitudinal edge and a second longitudinal edge (orthogonally to the direction of travel), can typically range from a few centimeters to 2 meters, depending on the metallic product to be stripped. For example, the width of the metallic product is between 50 cm and 2 meters, particularly between 75 cm and 1.5 meters.

[0073] After hot rolling, the metal product 3 is generally annealed and pickled in a facility not shown in Figure 1, before cold rolling.

[0074] This metal product 3 is fed through a conveyor at a speed typically up to 150 m / min, and, generally after being pickled, it passes through a cold rolling mill 4, which reduces its thickness to a value typically in the range of 0.2 to 15 mm in order to obtain a cold-rolled product. Following this cold rolling, the width of the metal product is typically between a few centimeters and 2 m, for example between 50 cm and 2 m, and in particular between 75 cm and 1.5 m.

[0075] The cold-rolled product then passes into an annealing furnace 5, where it is heated to a temperature of several hundred degrees, this temperature being adjusted according to the metallurgical objectives of the annealing. If this annealing is carried out (deliberately or accidentally) in the presence of a significant amount of an oxidizing gas such as oxygen, it leads to the formation of an undesirable oxide layer on the surface of the product 3. The composition, thickness, and adhesion of this oxide layer to the surface of the metal product 3 depend, in particular, on the composition of the metal product 3, the composition of the atmosphere in the furnace 5, the temperature in the furnace 5, and the residence time of the metal product 3 in the furnace 5.

[0076] According to the embodiment of Figure 1, the laser pickling installation 6 is arranged on the line after the annealing furnace 5.

[0077] This pickling installation 6 is intended to pickle an oxide layer present on the surface of the metal product 3, with a thickness generally between 0.1 and 30 pm.

[0078] The stripping installation 6 includes a stripping assembly 8.

[0079] The stripping assembly 8 includes at least one picosecond pulse laser device 10.

[0080] Each 10 picosecond pulsed laser device is configured to emit picosecond laser pulses onto the surface of the moving 3 metallic product to strip it.

[0081] The stripping assembly 8 further includes a control unit 12 for acquiring information relating to the moving metal product 3. This information includes the speed at which the metal product 3 moves and at least one characteristic dimension of the metal product 3 in a plane orthogonal to an axis of movement of the metal product, in particular the width of the metal product 3.

[0082] In one embodiment, the installation further includes a determination system configured to determine, on each of a plurality of successive sections of the moving metal product, an oxide layer expulsion energy density threshold. This density corresponds to the minimum energy required to expel the oxide layer on the section in question by a shock wave. The energy density threshold determination system is intended to evaluate the effective energy density required to remove the oxide layer from the moving strip using a single laser beam.

[0083] A section is, for example, a transverse band of a given length in the direction of product movement (also called longitudinal direction) and of equal width to that of the product.

[0084] The determination system includes a laser beam emission system, an image acquisition system, a processing system and a controller.

[0085] The laser pulse emission system includes at least one laser source capable of emitting laser pulses of a wavelength and pulse duration equal to that of the lasers which will be used for stripping.

[0086] The laser source is configured to emit an analytical laser beam onto a portion of the product surface as it moves across the surface. The energy density of this beam varies depending on the position within that portion. The energy density received at each point on the impacted portion is characterized by the energy density profile, or simply energy profile, of the beam. The energy profile thus associates each position, or a plurality of positions, within the plane of the product surface with a specific energy density emitted at that position.

[0087] The image acquisition system is configured to acquire, for each considered section of the product, an image of the portion impacted by the laser beams emitted by the emission system, during the movement of the product.

[0088] The processing system is configured to determine, from each image acquired by the image acquisition system, the expulsion energy density threshold of the oxide S exp , corresponding to the minimum energy density required to expel the oxide layer on the section considered.

[0089] The processing system includes, for example, an image analyzer and a threshold determination module. The image analyzer is configured to determine, by analyzing each acquired image as transmitted by the image acquisition system, at least one dimension of a stripped area of ​​the surface of the metallic product, i.e., an area free of oxide.

[0090] The threshold determination module is capable of determining, from information relating to the energy profile of the analysis beams and information relating to the stripped area, the expulsion energy density threshold of the oxide S exp To this end, the threshold determination module is capable of determining, from the energy profile of the analysis laser beam, what energy density led to the stripping to obtain the stripped area.

[0091] The control unit 12 is configured to determine, based on information relating to the moving metal product 3, and where applicable the determined energy density threshold, operating parameters to be imposed on the stripping assembly 8 to obtain the stripping of the oxide layer on the surface of the metal product 3 by emission by the laser device or each laser device 10 of picosecond laser pulses on the surface of the metal product 3.

[0092] In particular, when an expulsion energy density threshold is determined, the control unit 12 is configured to determine the operating parameters to be imposed on the stripping assembly as a function of this density threshold, so that each point of the section under consideration is exposed in at least one instant to an energy density greater than or equal to the expulsion energy density threshold of the oxide.

[0093] The control unit 12 is further configured to impose these operating parameters on the stripping assembly 8 to strip the surface of the metal product 3.

[0094] Each 10 picosecond pulsed laser device is configured to emit picosecond laser pulses of duration between 0.1 and 30 ps, ​​in particular between 1 and 30 ps, ​​preferably between 8 and 10 ps.

[0095] Preferably, the stripping assembly 8 includes a distribution system 14 configured to shape the laser pulses and / or to move the laser pulses over the surface of the moving metal product 3 such that the laser pulses emitted by the laser device or each laser device 10 strip the oxide layer over the entire surface of the metal product 3 as it moves.

[0096] In particular, the distribution system 14 is configured to shape and possibly move the laser pulses on the surface of the metallic product 3 in such a way that the laser pulses impact the surface of the metallic product in a plurality of lines or spots, including straight, circular, rectangular or square shapes.

[0097] These lines or spots are contiguous or overlap in such a way that the entire surface of the metal product 3 is cleaned.

[0098] In one embodiment, the distribution system 14 includes, for each laser device 10, a shaping device 16, as well as a scanning device 18.

[0099] The shaping device 16 is configured to shape the laser pulses such that each laser pulse impacts the surface of the metal product 3 along the line or spot on the surface of the metal product 3, the energy density received along at least one direction on the line or spot being substantially uniform.

[0100] The shaping device 16 preferably includes a Diffractive Optical Element (DOE), a Refractive Optical Element (ROE), an MPLC (Multi-plane light conversion) device, a Powell lens or an optical homogenizer.

[0101] This shaping device 16 can, according to one embodiment, be integrated into the laser device 10.

[0102] Thus, the shaping device 16 is configured to shape the laser pulse, for example along a line, curve, broken or straight line, or a spot in particular of circular, rectangular or square shape.

[0103] Advantageously, the distribution system 14 includes, for each laser device 10, at least one scanning device 18, configured to move the pulses generated by the associated laser device 10, shaped by the shaping device 16, onto the surface of the metal product 3, at a predetermined scanning speed and scan pitch, such that the pulses emitted by each laser device 10 impact a predetermined portion of the surface of the metal product 3. As described above, this portion is, for example, a curved, broken, or straight line, or a spot, particularly one that is circular, rectangular, or square. During the scanning process, the lines or spots cover the entire surface of the metal product 3.

[0104] Each scanning device 18 includes, for example, at least one scanner, in particular a polygonal or galvanometric scanner.

[0105] The distribution system 14 further typically includes a focusing element 22, in particular a focusing lens such as an f-theta lens or flat-field lens or a parabolic mirror.

[0106] The focusing element 22 is configured to focus the shaped laser pulse onto the surface of the metallic product 3.

[0107] Preferably, the distribution system 14 and the focusing element 22 are such that the stripping assembly 8 has an energy density received from the stripping assembly 8 on each line or spot of the surface of the metallic product 3 between 0.02 and 0.8 J / cm² 2 , preferably between 0.05 and 0.6 J / cm 2 , particularly between 0.08 and 0.35 J / cm 2 .

[0108] Indeed, an energy density of less than 0.01 J / cm² 2 would be too weak to strip the oxide layer, while an energy density greater than 0.8 J / cm² 2would risk damaging the metal under the oxide layer, and would lead to a heating of the surface of the metal product 3, which we seek to avoid.

[0109] Such an energy density makes it possible to ablate the oxide layer without ablate the metal present under this layer and without generating heat on the surface of the metallic product 3.

[0110] According to an advantageous embodiment, the laser device or each laser device 10 is configured to alternately emit picosecond laser pulses along two separate optical paths, the laser device 10 comprises two distribution systems 14, and the scanning device 18 associated with the laser device 10 comprises at least two synchronized and phase-shifted polygonal or galvanometric scanners, configured to move the pulses alternately generated by the associated laser device 10 onto the surface of the metallic product 3.

[0111] Thus, any latency time of each scanner is neutralized, since during this latency time, laser pulses are emitted by the laser device 10 onto the surface of the metallic product 3 via the other scanning device 18 and the other scanner.

[0112] Alternatively, the laser device(s) 10 are configured to emit picosecond laser pulses along a single optical path, and the stripping assembly 8 includes an external module configured to generate, from these pulses, laser pulses emitted successively along two distinct optical paths. This external module includes, for example, an acousto-optic modulator (AOM) or an electro-optic modulator (EOM).

[0113] The operating parameters determined by the control unit 12 preferably include a pulse energy of the laser device(s) 10, a duration of the pulses received from the stripping assembly 8 on the surface of the metallic product 3, the scanning speed and / or the scanning step of the scanning device 18 and possibly focusing parameters.

[0114] Thus, from this information, the control unit 12 is able to control the stripping assembly 8 to adjust the frequency of the emitted laser pulses, the scanning step and the scanning speed of the scanning device 18, as well as the operating parameters of the shaping device 16 and the focusing element 22, so that the entire surface of the metal product 3 is stripped, without ablating the metal present under the oxide layer.

[0115] In another embodiment, not shown in Figure 1, the laser stripping assembly 6 includes at least two picosecond pulsed laser devices 10.

[0116] In this embodiment, the laser stripping assembly 6 includes at least one shaping device 16, each shaping device 16 being associated with a laser device 10, each shaping device 16 being configured to shape the laser pulses emitted by the associated laser device 10.

[0117] In this embodiment, the laser stripping assembly 6 is configured to emit at least two picosecond laser pulses and shape the laser pulses such that the shaped laser pulses impact the surface of the metal product 3 along a continuous line, from a first longitudinal edge to a second longitudinal edge of the metal product 3, to strip the oxide layer present on the continuous line. The continuous line thus extends across the width of the metal product 3.

[0118] The laser stripping assembly 6 is further configured so that each laser device 10 successively emits a plurality of picosecond laser pulses during the passing of the metal product 3, and each shaping device 16 is configured to shape the plurality of picosecond laser pulses such that the shaped laser pulses successively impact the surface of the metal product 3 along a plurality of continuous lines, over at least a portion of the length of the metal product 3 during the passing.

[0119] For example, during the scrolling of the metal product 3, each shaping device 16 is configured to shape the picosecond laser pulses emitted by the associated laser device 10 such that each shaped laser pulse impacts the surface of the metal product 3 on the continuous line from the first edge to the second edge.

[0120] Alternatively, each shaping device 16 is configured to shape the picosecond laser pulses emitted by the associated laser device 10 such that the shaped laser pulses each impact the surface of the metallic product 3 on a portion of a continuous line, the portions of continuous lines impacted by the shaped laser pulses jointly forming the continuous line.

[0121] In this embodiment, a scanning device 18 is not required.

[0122] We will now describe a stripping process for a moving metallic product 3, preferably implemented by a stripping installation 6 as described above. This process includes the acquisition, by a control unit 12 such as the one described above, of information relating to the moving metallic product 3.

[0123] This information includes the speed of movement of the metal product 3 and at least one characteristic dimension of the metal product in a plane orthogonal to a movement axis of the metal product 3. This dimension is usually the width of the metal product 3.

[0124] According to one embodiment, the process includes determining an expulsion energy density threshold for the oxide layer, with the stripping then being carried out according to the expulsion energy density threshold thus determined.

[0125] The step of determining an oxide layer expulsion energy density threshold includes the emission of analysis laser pulses of wavelength and pulse duration equal to those of the stripping laser(s) on a portion of the section under consideration, to form, within the portion, a stripped zone devoid of the oxide layer.

[0126] The moving section of the product then passes in front of the image acquisition system. The step of determining an expulsion energy density threshold then involves the acquisition system capturing an image of the portion of the surface impacted by the analysis laser beams. This image is transmitted to the processing system, which then determines, from this image, the expulsion energy density threshold of the S oxide. exp allowing the ablation of the oxide layer at each point with a single pulse, thanks to the formation of a shock wave

[0127] Determining the expulsion energy density threshold of the oxide S exp This includes determining, from the image, a dimension of the stripped area. This dimension is determined, for example, by the image analyzer 40. The determination of the oxide expulsion energy density threshold S expthen includes the determination, from the size of the stripped area, of the energy density threshold for expulsion of the oxide layer.

[0128] The expulsion energy density threshold is then transmitted to the emission system 20, in order to allow control of the power of the analysis laser beams emitted at later times so that the emission of the analysis laser beams at these later times effectively results in the stripping of part of the impacted portion, without damaging the metal.

[0129] The process then includes the determination by the control unit, from information relating to the moving metal product 3, and where appropriate the expulsion energy density threshold, of operating parameters, as described below, to be imposed on a stripping assembly 8 as described above, this stripping assembly 8 comprising at least one picosecond pulsed laser device 10, to obtain the stripping of the oxide layer on the surface of the metal product 3.

[0130] The process further includes the emission by the laser device or each laser device 10 of picosecond laser pulses onto the surface of the moving metal product 3 to strip it, according to the operating parameters determined by the control unit 12.

[0131] Preferably, the picosecond laser pulses emitted by the laser devices 10 have a duration between 0.1 and 30 ps, ​​in particular between 1 and 30 ps, ​​preferably between 8 and 10 ps.

[0132] In one embodiment, the stripping assembly 8 includes a distribution system 14 configured to shape the laser pulses and / or to move the laser pulses across the surface of the moving metal product 3. In this embodiment, the method comprises shaping and / or moving the laser pulses across the surface of the metal product 3 such that the laser pulses strip the oxide layer across the entire surface of the metal product 3 as it moves.

[0133] In particular, the distribution system 14 shapes and optionally moves the shaped laser pulses on the surface of the metallic product 3 so that the laser pulses impact the surface of the metallic product 3 in a plurality of lines, for example curved, broken or straight, or spots, in particular circular, rectangular or square.

[0134] According to one embodiment, the distribution system 14 comprises, for each laser device 10, at least one scanning device 18, configured to move the pulses generated by the associated laser device 10, shaped by the shaping device 16, onto the surface of the metal product 3, at a predetermined scanning speed and scan pitch, such that the pulses emitted by each laser device 10 impact a predetermined portion of the surface of the metal product 3. As described above, this portion is, for example, a curved, broken, or straight line, or a spot, particularly one that is circular, rectangular, or square. During the scanning process, the lines or spots cover the entire surface of the metal product 3.

[0135] In this embodiment, the method thus comprises shaping the laser pulses by each shaping device 20 and scanning the shaped pulses, such that the shaped pulses impact the surface of the metal product 3 along a curved, broken, or straight line, or a spot, in particular circular, rectangular, or square in shape, the energy density received along at least one direction on the line or spot being substantially uniform. During scanning, the lines or spots cover the entire surface of the metal product 3. Furthermore, the focusing element 22 focuses the shaped pulse onto the surface of the metal product 3.

[0136] The energy density received from the entire stripping system on each line or spot of the metal product surface is between 0.01 and 0.8 J / cm² 2 , preferably between 0.05 and 0.6 J / cm 2 , particularly between 0.08 and 0.35 J / cm2 .

[0137] Such an energy density makes it possible to ablate the oxide layer without ablation or damage to the metal present beneath this layer.

[0138] Preferably, the movement of laser pulses on the surface of the metal product 3 is implemented by at least one scanning device 18 as described above, and the scanning device 18 moves the pulses generated by the associated laser device 10 onto the surface of the metal product 3, according to a determined scanning speed and scanning step, such that the pulses emitted by each laser device 10 impact a predetermined portion of the surface of the metal product 3.

[0139] According to one embodiment, the laser device or each laser device 10 emits picosecond laser pulses alternately along at least two separate optical paths, the scanning device 18 comprises at least two synchronized and phase-shifted polygonal or galvanometric scanners, and the polygonal or galvanometric scanners alternately move the pulses generated by the laser device 10 on the surface of the metal product 3 into separate positions on the surface of the metal product 3.

[0140] Alternatively, the laser device(s) 10 emit picosecond laser pulses along a single optical path, and the stripping assembly 8, comprising an external module, generates, from these pulses, laser pulses emitted successively along two distinct optical paths. This external module includes, for example, an acousto-optic modulator (AOM) or an electro-optic modulator (EOM).

[0141] Preferably, the operating parameters include a pulse energy of the laser device or each laser device 10, a duration of the pulses received from the stripping assembly 8 on the surface of the metallic product 3, the scanning speed and / or scanning pitch of the scanning device 18, and focusing parameters.

[0142] In another embodiment, as described above, the stripping assembly 8 comprises at least two picosecond laser devices 10, each configured to emit picosecond laser pulses, and at least two shaping devices 16, each associated with one of the laser devices 10, each shaping device 16 being configured to shape the laser pulses emitted by the associated laser device 10. In this embodiment, the method comprises the emission, by each laser device 10, of picosecond laser pulses and the shaping of the laser pulses such that the shaped laser pulses impact the metal product 3 along a continuous line, from the first edge to the second edge of the metal product 3, to strip the oxide layer present on the continuous line.

[0143] During the scrolling of the metal product 3, the process includes the emission of a plurality of picosecond laser pulses by each laser device 10 and the shaping of the laser pulses such that the shaped laser pulses impact the surface of the metal product 3 in a plurality of continuous lines, over at least a portion of the length of the metal product 3 to strip it.

[0144] As an example, during the scrolling of the metal product 3, the laser pulse emitted by each laser device is shaped so that each shaped laser pulse impacts the surface of the metal product 3 along the continuous line.

[0145] According to another example, during the scrolling of the metal product 3, the laser pulses emitted by the laser devices are shaped such that the shaped laser pulses each impact the surface of the metal product 3 along a portion of the continuous line, the portions of continuous lines impacted by the shaped laser pulses together forming the continuous line from the first edge to the second edge of the metal product 3.

[0146] Furthermore, the focusing element 22 focuses the shaped laser pulses onto the surface of the metallic product 3.

[0147] The installation and process according to the invention make it possible, through the use of picosecond pulses, to ablate the oxide layers while avoiding the thermal charges observed during the use of conventional lasers, and thus to avoid the formation of a new oxide layer after stripping, which would require additional stripping.

[0148] The process described above applies not only to products in strip form but also to products such as long products (such as wires), or metal tubes.

[0149] In particular, for wire stripping, reference can be made to the installation described in application WO2023152548.

Claims

DEMANDS 1. Installation for stripping (6) a moving metallic product (3), the moving metallic product (3) having at least one surface covered with an oxide layer, characterized in that the installation (6) comprises: - a stripping assembly (8) comprising at least one picosecond pulsed laser device (10), each picosecond pulsed laser device (10) being configured to emit picosecond laser pulses onto the surface of the moving metallic product (3) to strip it, - a control unit (12) suitable for acquiring information relating to the moving metal product (3), the information including a speed of movement of the metal product (3) and at least one characteristic dimension of the metal product (3) in a plane orthogonal to an axis of movement of the metal product (3), the control unit (12) being configured to: - determine operating parameters to be imposed on the stripping assembly (8) to obtain the stripping of the oxide layer on the surface of the metallic product (3) by emission by the laser device(s) (10) of picosecond laser pulses on the surface of the metallic product (3), - impose said operating parameters on said stripping assembly (8) to strip the surface of the metal product (3).

2. Stripping installation (6) according to claim 1, in which the picosecond laser pulses have a duration of between 0.1 and 30 ps, ​​in particular between 1 and 30 ps.

3. Pickling installation according to any one of claims 1 or 2, wherein the control unit (12) is configured to determine the operating parameters to be imposed on the pickling assembly (8) to achieve pickling by expulsion of the oxide layer on the surface of the metal product (3) by a single pulse at each treated point of the surface, said operating parameters being imposed on said pickling assembly (8) to pickle the surface of the metal product (3) by expulsion of the oxide layer by the emission of a single pulse at each of said treated points of the surface.

4. Pickling installation (6) according to claim 3, further comprising a determination assembly configured to determine, on each of a plurality of successive sections of the passing metal product (3), a density threshold expulsion energy of the oxide layer, corresponding to a minimum energy density required to expel the oxide layer on the section considered by a single laser pulse, the control unit (12) being configured to receive the expulsion energy density threshold, to determine the operating parameters to be imposed on the stripping assembly as a function of this density threshold, such that each point of the section considered is exposed in at least one instant to an energy density greater than or equal to the expulsion energy density threshold of the oxide layer, and to control the emission by the stripping assembly (8), of laser pulses of energy greater than or equal to the expulsion energy density threshold.

5. Stripping installation (6) according to claim 4, wherein the determination assembly comprises: an emission system including a laser source, the emission system being configured to emit, on a portion of said section considered, laser beams of analysis with wavelength and beam duration equal to those of the laser stripping device(s), to form, within said portion, a stripped zone devoid of the oxide layer; an image acquisition system configured to acquire an image of the portion impacted by the laser beams of analysis, during the passage of the metallic product (3); a processing system configured to determine, from each image acquired by the image acquisition system, a representative dimension of the stripped zone and to evaluate, from said representative dimension and information relating to the energy profile of the laser beams of analysis,the oxide layer expulsion energy density threshold.

6. Stripping installation (6) according to any one of claims 1 to 5, wherein the stripping assembly (8) includes a distribution system (14) configured to shape the laser pulses and / or to move the laser pulses over the surface of the moving metal product (3) such that the laser pulses emitted by the laser device(s) (10) strip the oxide layer over the entire surface of the moving metal product (3).

7. Stripping installation (6) according to claim 6, wherein the distribution system (14) is configured to shape and move the laser pulses on the surface of the metallic product (3) such that the laser pulses impact the surface of the metallic product (3) according to a plurality of lines, in particular straight, curved or broken, or spots, in particular circular, rectangular or square in shape.

8. Stripping installation (6) according to claim 7, wherein the distribution system (14) comprises, for each laser device (10), at least one shaping device (16), preferably a Diffractive Optical Element (DOE), a Refractive Optical Element (ROE), an MPLC (Multi-plane light conversion) device, a Powell lens or an optical homogenizer, configured to shape the laser pulses such that each laser pulse impacts the surface of the metal product (3) along the line or spot on the surface of the metal product (3), the energy density received along at least one direction on the line or spot being substantially uniform.

9. A stripping installation (6) according to any one of claims 7 or 8, wherein the stripping assembly (8) is configured such that the energy density received from the stripping assembly (8) on each line or spot of the surface of the metal product (3) is between 0.01 and 0.8 J / cm² 2 , particularly between 0.08 and 0.35 J / cm 2 .

10. Stripping installation (6) according to any one of claims 6 to 9, wherein the distribution system (14) comprises, for each laser device (10), at least one scanning device (18), configured to move the pulses generated by the associated laser device (10) onto the surface of the metal product (3), according to a determined scanning speed and scanning pitch, such that the pulses emitted by each laser device (10) affect a predetermined portion of the surface of the metal product.

11. Stripping installation (6) according to claim 10, wherein each scanning device (18) comprises at least one scanner, in particular a polygonal or galvanometric scanner.

12. A stripping installation (6) according to any one of claims 10 or 11, wherein the distribution system (14) comprises, for each laser device (10), at least one shaping device (16), configured to shape the laser pulses such that each laser pulse impacts the surface of the metal product (3) along the line or spot on the surface of the metal product (3), the energy density received along at least one direction on the line or spot being substantially uniform, the distribution system (14) includes a focusing element (22), in particular a focusing lens such as an f-theta lens, or a parabolic mirror, configured to focus the shaped laser pulse onto the surface of the metallic product (3), the scanning device (18) being disposed between each shaping device (16) and the focusing element (22).

13. Stripping installation (6) according to any one of claims 10 to 12, wherein the laser device or each laser device (10) is configured to alternately emit picosecond laser pulses along two separate optical paths, and the scanning device (18) associated with the laser device (10) comprises at least two synchronized and phase-shifted polygonal or galvanometric scanners, configured to move the pulses alternately generated by the associated laser device (10) onto the surface of the metallic product (3).

14. Stripping installation (6) according to any one of claims 10 to 12, wherein the laser device or each laser device (10) is configured to emit picosecond laser pulses along a single optical path, and the stripping assembly (8) includes an external module, in particular an acousto-optic modulator (AOM) or an electro-optic modulator (EOM), configured to generate, from the laser pulses, laser pulses emitted successively along two separate optical paths.

15. Stripping installation (6) according to any one of claims 10 to 14, wherein the operating parameters include a pulse energy of the laser device(s) (10), a duration of the pulses received from the stripping assembly (8) on the surface of the metal product (3), the scanning speed and / or the scanning pitch of the scanning device (8).

16. A method for pickling a metal product (3) in a continuous flow, the metal product (3) in a continuous flow having at least one surface covered with an oxide layer, characterized in that it comprises: - the acquisition, by a control unit (12), of information relating to the moving metallic product (3), the information including a speed of movement of the metallic product (3) and at least one characteristic dimension of the metallic product (3) in a plane orthogonal to an axis of movement of the metallic product, - the determination of operating parameters to be imposed on a stripping assembly (8) comprising at least one picosecond pulsed laser device (10), to obtain the stripping of the oxide layer on the surface of the metallic product (3), - the emission by the picosecond pulsed laser device or devices (10), of picosecond laser pulses on the surface of the moving metallic product (3) to strip it, according to the operating parameters determined by the control unit (12).

17. Stripping method according to claim 16, wherein the picosecond laser pulses have a duration of between 0.1 and 30 ps, ​​in particular between 1 and 30 ps.

18. A pickling method according to any one of claims 16 or 17, wherein the operating parameters to be imposed on the pickling assembly (8) are determined so as to obtain pickling by expulsion of the oxide layer on the surface of the metal product (3) by a single pulse at each treated point of the surface, and said operating parameters are imposed on said pickling assembly (8) to pickle the surface of the metal product (3) by expulsion of the oxide layer by a single pulse at each treated point of the surface.

19. Pickling method according to any one of claims 16 to 18, wherein the determination of operating parameters includes, on each of a plurality of successive sections of the metal product (3) in motion, the determination of an expulsion energy density threshold of the oxide layer on the section considered of the metal product (3), corresponding to a minimum energy density required to expel the oxide layer on the section considered, the determination of the operating parameters to be imposed on the pickling assembly (8) including said energy density threshold, such that each point of the section considered is exposed in at least one instant to an energy density greater than the expulsion energy density threshold of the oxide layer.

20. A method according to claim 19, wherein the determination of the energy density threshold comprises: - emission of laser beams for analysis by an emission system comprising a laser source, the laser beams for analysis being of equal wavelength and beam duration to those of the laser stripping device(s), on a portion of the section considered, to form, within the portion, a stripped zone devoid of the oxide layer, - capture of an image of the portion of the surface impacted by the laser scanning wells, - determination, from said image, of a dimension representative of the stripped area, - evaluation, from said representative dimension and information relating to the energy profile of the analysis laser sources, of the expulsion energy density threshold of the oxide layer.

21. A stripping method according to any one of claims 16 to 20, wherein the stripping assembly (8) includes a distribution system (14) configured to shape the laser pulses and / or to move the laser pulses over the surface of the metal product (3) as it is being moved, the method includes shaping and / or moving the laser pulses over the surface of the metal product (3) such that the laser pulses strip the oxide layer over the entire surface of the metal product (3) as it is being moved.

22. Stripping method according to claim 21, wherein the distribution system (14) shapes and / or moves the laser pulses on the surface of the metal product (3) such that the laser pulses impact the surface of the metal product (3) in a plurality of lines, in particular straight, curved or broken, or spots, in particular circular, rectangular or square in shape.

23. A stripping method according to claim 22, wherein the distribution system (14) comprising, for each laser device (10), a focusing element (22), in particular a focusing lens, such as an f-theta lens, or a parabolic mirror, the method comprises focusing, by the focusing element (22), the shaped pulses, such that the shaped and focused pulses impact the surface of the metallic product (3) along the line or the spot.

24. A stripping method according to any one of claims 22 or 23, wherein the distribution system (14) comprises, for each laser device (10), at least one shaping device (16), the shaping device (16) preferably comprising a Diffractive Optical Element (DOE), a Refractive Optical Element (ROE), an MPLC (Multi-plane light conversion) device, a Powell lens or an optical homogenizer, the method comprises shaping the laser pulses by each shaping device (16) such that the shaped pulses impact the surface of the metallic product (3) along the line or the spot, the energy density received along at least one direction on the line or the spot being substantially uniform.

25. A pickling method according to any one of claims 22 to 24, wherein the energy density received from the pickling assembly (8) on each line or spot of the surface of the metal product (3) is between 0.01 and 0.8 J / cm² 2 , particularly between 0.08 and 0.35 J / cm 2 .

26. Stripping method according to claim 24, wherein a displacement of laser pulses shaped on the surface of the metal product (3) is implemented by at least one scanning device (18), the scanning device (18) moving the pulses generated by the laser device (10) and shaped by the associated shaping device (16) on the surface of the metal product, according to a determined scanning speed and scanning step, such that the pulses emitted by each laser device (10) impact a portion of the surface of the metal product (3).

27. A stripping method according to claim 26, wherein the laser device or each laser device (10) emits picosecond laser pulses alternately along at least two distinct optical paths, the scanning device (18) comprises at least two synchronized and phase-shifted polygonal or galvanometric scanners, and the polygonal or galvanometric scanners alternately move the pulses generated by the laser device (10) onto the surface of the metal product (3) into distinct positions on the surface of the metal product (3).

28. Stripping method according to claim 26, wherein the laser device or each laser device (10) is configured to emit picosecond laser pulses along a single optical path, and the stripping assembly (8) includes an external module, in particular an acousto-optic modulator (AOM) or an electro-optic modulator (EOM), generating, from the laser pulses, laser pulses emitted successively along two distinct optical paths.

29. Stripping method according to any one of claims 26 to 28, wherein the operating parameters include a pulse energy of the laser device or each laser device (10), a duration of the pulses received from the stripping assembly (8) on the surface of the metal product (3), the scanning speed and / or the scanning pitch of the scanning device.

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